The present invention relates to a method for sterilizing soils and to the equipment related thereto.
The growing specialization in crops and the so-called single-crop systems, particularly widespread in the sector of ornamental plants, garden vegetables, corn and beet, generate a strong interaction between the microflora of the soil and the radical system of the plants.
Moreover, numerous vegetable and animal parasites can survive in the soil even for many years, until they come in contact with plants prone to suffer from their pathogenetic action.
The continued cultivation of such plants in the same soil thus leads to ailments in their growth and to a progressive deterioration in harvest yields. The first and most ancient way to obviate this problem consists of the so-called "crop rotation" or, more generally, of prolonging the interval during which a crop remains absent from a soil. In this situation, the soil dwelling parasites of the plant itself progressively die due to "starving".
However, there are cases wherein the "rotation" method does not provide sufficient reliability: many parasites are able to survive as parasites of other plants or remaining in a state of quiescent life; other times, abandoning a certain crop for a given period may not be economically advantageous. It is then necessary to resort to rather energetic interventions, which must therefore be applied only on the bare soil, some time before planting a new crop. These are rather onerous processes that accomplish the disinfection or disinfestation by means of chemical or physical interventions.
Chemical interventions consist of the administration of fungicides, insecticides, plant protection products or fumigation products: such intervention are long, very costly and highly hazardous for environmental pollution. After their execution, rather long time intervals are required before it is possible to proceed with the cultivation of the treated soil.
Physical interventions essentially consist of administering heat to the soil, heat which can be produced and distributed in various ways. As a rule, regardless of the methods used, heating the soil up to 80-90.degree. C. is sufficient to kill all parasites present. This type of operation allows to start cultivation a short time afterwards, as soon as the temperature of the soil drops to 25-30.degree. C.
Among physical interventions, treatments with dry heat, performed by heating the soil in the so-called country ovens, are the least effective ones, both because the results they yield are not always satisfactory, and because in any case they can only be applied to small plots of land.
Sterilization with boiling water entails prohibitive expenses and it is only plausible for very small plots of land.
Steam treatment finds applications for soil disinfection in greenhouses, stable seed-beds or small open plots: it can be accomplished both introducing the soil into large cement tanks, or in other containers, then passing through the soil both the steam produced by a generator and fixed or movable tools positioned on or within the soil to be disinfected.
In this latter case, the steam, produced by an appropriate generator, moves through pipes which lead it to the aforesaid dispensing tools of various designs. Use is made of hood dispensers, similar to upside down cases or to canvas sheets with the edges stuck in the soil, wherein the steam is inserted, or even comb dispensers, comprising a horizontal pipe wherefrom a series of vertical pipes depart which convey the steam into the soil. Hood dispensers are particularly indicated when the sterilization has to reach depths in the order of 20-25 cm, comb dispensers for greater depths. Lastly it is possible to use large self-propelled machines, able to intervene autonomously.
Only sufficiently profitable cultivations, for instance floriculture, justify the use of this system which presents, for wide open spaces, logistically insurmountable difficulties.